The present invention relates in general to crash attenuators, and more particularly to medium-damped crash attenuators that use the flow of a medium such as a liquid or gas to dissipate the energy of an object such as a vehicle impacting the crash attenuator. Still more particularly, the invention relates to attenuators enabling active control of the rate of energy dissipation thereof to better control the deceleration of vehicles impacting the attenuator having widely varying kinetic energy.
The present invention also relates to method for protecting fixed structures from damage caused by the impact of objects such as vehicles, e.g., structures situated alongside highways.
Many commercial products exist and numerous patents have been issued directed to the design and construction of impact attenuators or barriers to control the deceleration of an errant vehicle as it approaches an obstruction or hazard on, or adjacent to, a highway. Several prior art patents will be discussed below. This invention is concerned primarily with impact attenuators that are mounted on the rear of a construction vehicle, commonly called truck-mounted attenuators (TMA), although it is not limited thereto. The invention also has applicability to more permanent attenuator installations such as those of the type used around fixed highway structures especially where space is limited.
A review of some patents and commercial literature of TMAs illustrates a wide variety of designs which appear to have evolved by trial and error with little attempt to optimize the design to handle a wide variety of impacting vehicle kinetic energies. Thus, such existing devices generally have a fixed force versus deflection function that provides the same resisting force to the impacting vehicle regardless of that vehicle""s mass or velocity.
The primary purpose of a TMA is to protect construction personnel from death or injury caused by a vehicle which mistakenly or accidentally intrudes into a construction zone. Secondarily, the TMA is designed to minimize the death and injury to the occupants of the errant vehicle. Ideally, the TMA should capture the impacting vehicle preventing it from being diverted either into adjacent traffic or off the road where it might impact a roadside structure such as a utility pole. Preferably, the TMA should even decelerate the vehicle at an acceptable level, such as 15 Gs, regardless of the mass or velocity of the impacting vehicle. Additionally, it is desirable for the TMA to be low cost, reusable after an impact, easily transported, light weight, easily shipped, easily stored, etc. No TMA on the market today satisfactorily meets all of these requirements. Therefore, there is a dire need for such a TMA that is the subject of this invention.
It is clear from the patents and commercial literature that many mechanisms exist for absorbing energy of an impacting vehicle into a TMA. These include a variety of structures that depend on the bending of metal or plastic, devices that utilize water, foam rubber, plastic etc. in a variety of energy absorption modes. Frequently, the energy dissipated by the system is part of the structure of the device. In fact, the prior art inventions have frequently confused the functions of structure and energy absorption. The instant invention therefore centers on the separation of these two functions of supporting structure and energy dissipation and optimizing these functions separately.
The basic problem to be solved by a TMA design is to capture an impacting vehicle and to decelerate it at an approximate constant value that is relatively independent of the velocity and mass of the impacting vehicle. It is also desirable for the impactor to be resetable and that it can be easily collapsed for transportation, shipping, storage etc. It is noteworthy that none of the TMAs on the market today are reusable and therefore invariably require replacement after an impact.
Review of the prior art:
U.S. Pat. No. 3,674,115 to Young et al. describes a liquid filled shock absorber comprised of many tubes each with a fixed orifice. On impact of a vehicle into the shock absorber, the fluid is forced to flow through the orifices which provides the energy dissipation. Since the orifices are fixed, the system will not adjust to vehicle impacts of varying kinetic energy to provide a constant deceleration. Also, since the device is substantially composed of such cylinders, it is heavy if used as a TMA. It is designed, therefore, for use in fixed installations.
U.S. Pat. No. 4,190,275 to Mileti describes a light weight reusable TMA which is self restoring and thus immediately available to receive an additional impact. The impact attenuator is constructed from a plurality of expanded plastic sheets sandwiched between plywood stiffeners. The expanded plastic sheets form air filled cells. The energy dissipation mechanism is not disclosed but it appears that the energy is stored as compressed gas within the cells rather than dissipated. Thus, there is a substantial force at the end of the crash to cause the impacting vehicle to change its direction and rebound at a substantial velocity off of the TMA thus substantially increasing the velocity change of the vehicle above the initial vehicle impact velocity. This increases the severity of the crash and thus the potential for injury to the construction crew and the vehicle occupants. There is no provision in this patent to adjust the force on the impacting vehicle so that substantially the same deceleration is achieved for vehicles of different kinetic energy. This has the effect of substantially increasing the length required of the device in order to handle both light and heavy impacting vehicles at high velocities. The first part of the TMA must be designed to decelerate a light, high speed vehicle at a safe level. This same force is then all that is available for the heavy vehicle which is then decelerated at a much lower level during the initial part of the crush and then at a higher level later.
U.S. Pat. No. 4,635,981 to Friton describes an attenuator including a series of chambers made from sheet metal with some of the chambers containing crushable plastic foam, which, along with the plastic deformation of the sheet metal, dissipates the kinetic energy of the impacting vehicle. The system is not reusable and does not adjust to impacting vehicles having different kinetic energies.
U.S. Pat. No. 4,674,911 to Gertz describes a crash cushion which uses the compression of air to act as a spring to provide an ever increasing force acting against the impacting vehicle. This system is reusable but does not adjust to impacting vehicles having different kinetic energies. By having the function of an ever increasing force with displacement, it is particularly inefficient in decelerating a vehicle where a constant force is desired.
U.S. Pat. No. 4,711,481 to Krage et al. describes an attenuator that uses the crushing or plastic deformation of sheet metal to provide the energy dissipation. This system is not reusable and does not adjust to impacting vehicles having different kinetic energies. By having the function on an ever increasing force with displacement, it is particularly inefficient in decelerating a vehicle where a constant force is desired.
U.S. Pat. No. 5,052,732 to Oplet et al. describes an attenuator which uses a plurality of layers of fibrous hexagonal elongate cells which provides energy absorption during crushing. It suffers from the same defects at Krage et al. (U.S. Pat. No. 4,711,481).
U.S. Pat. No. 5,101,927 (Murtuza) describes an automatic brake actuation device including a xe2x80x9cfeelerxe2x80x9d which extends forward of a vehicle and detects objects that the vehicle is about to strike. Upon detecting an object, the device actuates the brakes of the vehicle to bring the vehicle to rest. Also, upon impact with the object, the feeler is retracted without applying any force against such retraction. One stated object of the Murtuza invention is to provide an improved automatic brake actuation system wherein the extendable detector is retracted upon impacting an object. More particularly, in the embodiment shown in FIGS. 13 and 14, the device includes a support member 112 mounted to the vehicle and a feeler cylinder 114 having a piston 118 therein. Movement of the piston 118 controls expansion and retraction of a parallel-bar expanding feeler 130. Movement of the piston is obtained by forcing fluid into a retracting portion 128 of the cylinder 114 while fluid is vented from the extending portion 126 and vice versa. This is achieved by providing fluid controls to act as extending means or devices and retracting means or devices for supplying fluid under pressure to the feeler cylinder.
U.S. Pat. No. 5,192,157 to Laturner describes a fixed installation vehicle crash barrier that attempts to make use of a more efficient method of deforming metal to absorb energy. It also suffers from the same limitations as Krage et al. (U.S. Pat. 4,711,481).
U.S. Pat. No. 5,199,755 to Gertz describes a TMA that also uses the bending of metal as the main energy absorption mechanism and thus has the same limitations as Krage et al. (U.S. Pat. 4,711,481).
U.S. Pat. No. 5,403,112 to Carney describes a TMA where part of the structure is a scissors mechanism. The bending of metal is the energy absorption mechanism and thus has the same limitations as Krage et al. (U.S. Pat. 4,711,481).
U.S. Pat. No. 5,642,792 to June describes a TMA using large drum shaped plastic cylinders to provide an energy absorption system. The system is not reusable and does not adjust to the kinetic energy of the impacting vehicle.
Accordingly, none of the prior art patents mentioned above discloses a TMA having the sought after properties and thus, a critical need exists for such a device. A central issue is that since prior art TMAs are not optimally designed, they must be made very long in order to handle both low and high mass vehicles at high speed. This makes the devices expensive, difficult to maneuver and less than optimum as a life saving device.
It is an object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure.
It is another object of the present invention to provide a new and improved crash attenuator for mounting on a truck of stationary structure which is reusable.
It is another object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure which adjusts to the kinetic energy of a vehicle impacting into the same.
It is still another object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure which is efficient in decelerating a vehicle impacting into the attenuator where a constant deceleration is desired.
It is yet another object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure that separates the functions of the supporting structure and the energy dissipation and optimizes these functions separately.
It is another object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure which enables active control of the rate of energy dissipation in order to better control the deceleration of vehicles impacting the attenuator having widely varying kinetic energy.
It is a further object of the present invention to provide a new and improved crash attenuator for mounting on a truck or a stationary structure which is low cost, reusable after an impact, easily transported, light weight, easily shipped and easily stored.
The crash attenuators in accordance with this invention are first designed as a structural mechanism which is capable of supporting the loads arising from the impact of a vehicle and the resulting reaction loads arising from the truck inertial loading and the energy dissipation or damping device. The damping device is then designed which may be either one or more hydraulic cylinders and/or one or more inflatable/deflatable airbags. This separates the structural function from the energy dissipation function and permits the optimization of each separately. In both cases, a movable displacement structure is provided to enable movement of a bumper having an impact-receivmg face toward and away from a frame connected to the truck or stationary structure. The displacement structure may comprise a scissors mechanism that has an expanded condition in which the bumper is distant from the frame and a contracted condition in which the bumper is relatively close to the frame. Similar scissors mechanisms have found a successful application for cases of load lifting in industrial settings. The energy dissipation device is coupled to the scissors mechanism and can be either hydraulic or pneumatic, although the hydraulic design is preferred for most applications.
This approach was only partially implemented in U.S. Pat. No. 5,248,129 to Gertz wherein a scissors mechanism is coupled with energy absorbing elements and in U.S. Pat. No. 5,642,792 to June wherein a hinged support frame supports an energy absorbing rectangular box-like structure. The preferred design of a crash attenuator in accordance with the invention combines a scissors or other expandable structure containing a plurality of sections, preferably at least three or four sections, with hydraulic damping cylinders. In a second design of a crash attenuator in accordance with the invention, the scissors mechanism houses at least one inflatable airbag which may be in the form of an accordion structure with the various sections of the airbag internally tethered for shape retention. Other shape retention means may also be provided in connection with the airbag(s).
An electronic control module may be incorporated onto the scissors mechanism in order to sense the motion of an impacting vehicle and control the opening of exhaust orifices associated with the hydraulic or pneumatic energy dissipation device in order to achieve a substantially constant deceleration of the vehicle regardless of the mass and velocity of the impacting vehicle. The cross section area of the airbag(s) will be made as large as possible in the pneumatic case in order to minimize the initial compression of the airbag(s) before maximum pressure is obtained. The motion sensing system may be ultrasonic, radar or lidar based, or preferably accelerometer based. An electronically controlled valve is used to control the flow of either the hydraulic fluid or other medium from hydraulic cylinders in the hydraulic case, or gas or other medium out of the airbag(s) for the pneumatic case, during impact.
The system functions as follows. In the collapsed state, the TMA will occupy a space of typically approximately 25% of its expanded state maling it easy to transport, store and ship. It could occupy any amount less than about 50% of its expanded state. This is facilitated by the use of a scissors mechanism comprises linked members articulated to one another. Upon arrival at the work site, a hydraulic pump in the hydraulic case, or small vacuum cleaner type pump for the pneumatic case, will be activated to expand the TMA to its extended state where it is ready to receive an impact. The scissors mechanism will thus be expanded as the hydraulic pump is actuated to extend pistons associated therewith, the cylinder and piston of each hydraulic cylinder being connected to different parts of the scissors mechanism, or the airbag(s) is(are) inflated.
Bumpers at the end of the TMA, made from a material such as polyurethane foam, provide a low level of energy absorption for low speed impacts. At higher speeds, a deformable subbumper structure can be used to help channel the vehicle into the center of the TMA and capture it to prevent it from being deflected off of the TMA. Accelerometers located in the rear of the bumper structure sense the deceleration of the bumper, and thus the deceleration of the impacting vehicle. These accelerometers send signals to the control module, which then adjusts the valve or orifice openings to control the fluid outflow from the hydraulic cylinders or medium outflow from the airbag(s) and thereby vary the energy dissipation force provided by the energy dissipation device and as a result, the vehicle deceleration. In the hydraulic embodiment, the rate of fluid outflow will be reflected in the movement of the piston back into the cylinder. In this manner, the system will provide a large energy dissipation force when the impacting vehicle is a heavy vehicle and a lower energy dissipation force for light vehicles, thus approximately stopping both types of vehicles in the same distance for the same velocity of impact. This permits a more efficient utilization of the available crush space and thus minimizes the size of the TMA.
Some loss of efficiency results from the initial compressibility of the gas in the airbag for the pneumatic case. However, calculations set forth in Appendix 1 show that this loss of efficiency is manageable without greatly increasing the length of the TMA if atmospheric pressure is used. To the extent that the airbag can be pressurized, this effect will become smaller. Other energy absorption mechanisms that provide a force in parallel at least during the compression stage can of course be added to help compensate for this compressibility effect.
Another concern of the pneumatic system is in the compliance of the airbag itself Once again, calculations indicate that this should not be a significant problem if the airbag is properly designed. In some cases, an accordion design with simple tethering will prove to be insufficient and a design based on a self-shaping airbag design, as disclosed in U.S. Pat. No. 5,653,464 incorporated herein by reference, which solves the problem by properly shaping the airbag to cause it to naturally take on the desired shape.
Although the preferred design uses electronics to control the valve associated with the hydraulic cylinders or orifice opening(s) associated with the airbag(s), other variations include the use of a mechanical system to sense the acceleration and control the opening of the flow restrictors, i.e., the valve or orifice openings. This results in an all-mechanical system by eliminating the electronics. The all-mechanical system is particularly applicable for fixed installations in addition to truck mounted applications.
In one method for protecting a truck or fixed structure in accordance with the invention, a movable displacement structure is mounted to the truck or structure and has an expanded position and a contracted position. A bumper having an impact-receiving face adapted to receive an impact from an object in a crash is arranged on the displacement structure. The displacement structure is preferably stored and transported in its contracted condition and when readied for use, it is expanded to its expanded position. In use, impact of an object into the bumper which causes the displacement structure to be moved from the expanded position toward the contract position is sensed and at least some, if not all, of the impact energy of the object is dissipated by adjusting an energy dissipation force such that the object is brought to rest. In some preferred embodiments, the displacement structure may be expanded after the impact energy of the object is dissipated such that the crash attenuator is reusable.
It is possible to sense deceleration of the object after impact into the bumper and adjust the energy dissipation force based on the sensed deceleration of the object. The hydraulic and pneumatic systems described herein may be applied.